But of all biometric categories, finger-scan technology is showing the greatest downward trend in cost and size, industry observers say. The advent of tiny, silicon-based fingerprint sensors is the impetus here. "In finger-scan, the direction is smaller and smaller sensors to drive down the cost of the device," said Trevor Prout, director of marketing at the International Biometric Group LLC.

AuthenTec Inc., for example, has created a silicon fingerprint sensor that measures .384 inches x .032 inches, about the size of a fingertip, and costs $6 per unit. The sensor is designed for personal digital assistants, wireless phones and other small products.

Diminutive fingerprint sensors may soon be integrated on smart cards as well. Smart cards already are starting to carry biometric templates — unique digital codes that identify a person — but prototype cards also incorporate the biometric reader, according to Jeff Stapleton, manager of risk advisory services at KPMG LLP.

Eric Longo, a senior associate at KPMG, said the sensor-on-card approach has promise, but "hasn't been proven in real-world applications yet."